1. Field of the Invention
The present invention relates to the monitoring of communications receivers, and more particularly, to the monitoring of the channel to which a receiver is tuned.
2. Description of the Prior Art
In the entertainment field, the size of an audience enjoying an event or program is often monitored as an important indicator of popularity or success. This is particularly true with entertainment provided over electronic communications systems such as television and radio. The audience size is employed not only to determine the popularity of a particular program or show, but also to assist in making programming decisions. Furthermore, advertising rates are based upon audience size.
Determining the size of an electronic communications system audience is particularly difficult due to the dispersed nature of the audience. Heretofore, telephonic surveys have been conducted to determine the number of individuals watching particular radio or television programs. However, such surveys are highly labor intensive. Furthermore, the necessity of calling thousands of households makes such surveys time consuming.
To overcome problems associated with telephonic surveys, electronic monitoring techniques have been developed. Thus, U.S. Pat. Nos. 4,058,829 to Thompson and 4,044,376 to Porter teach television monitoring devices. According to these patents, a signal is injected into the radio frequency input of the television at a frequency corresponding to the carrier frequency of a particular channel. A probe attached to some point within the video circuits of the television determines whether the injected signal has passed through the tuner. If the injected signal has not passed through the tuner, then the frequency of the injected signal is changed to the carrier frequency of another channel and the determination is repeated. This process continues until a frequency is selected which enables the injected signal to pass through the tuner. The channel to which the television is tuned is then known.
See also U.S. Pat. Nos. 4,216,497 to Ishman et al and 2,630,367 to Rahmel which teach television monitoring systems.
Cable television systems are becoming more popular, and therefore more significant with respect to audience monitoring. FIG. 1 illustrates the typical arrangement of a cable television system. In FIG. 1, cables 100 and 102 are applied to cable converter 104. Each of cables 100 and 102 carries 65 channels in the present embodiment. The output of cable converter 104 is applied to television 106. Cable converter 104 may be in a separate housing which sits atop television 106. Cable converter 104 selects one of the 124 channels carried over cables 100 and 102 and adjusts the carrier frequency of the selected channel to a predetermined frequency, typically corresponding to the carrier frequency of channel 2, 3 or 4 on television. Cable converter 104 is, therefore, said to have a fixed, or single channel output. Thus, television 106 remains set on channel 2, 3 or 4, as specified by the cable TV company, and channel selection is done at cable converter 104 by tuning to a particular carrier frequency on one of cables 100 and 102.
Electronic channel detectors have also been developed which are particularly suited for cable television systems. Examples of such detectors are disclosed in U.S. Pat. Nos. 4,048,562 to Haselwood et al, 3,769,579 to Harney, 3,230,302 to Bruck et al and 3,987,397 to Belcher et al.